1. Field of Invention
The present invention relates to a system and method of the waste treatment, and more particularly to a flue-gas purification and reclamation system and method, which has high efficient removal rate of pollutants or contaminations in the wastes of flue-gas and to remove two or more contaminations within the flue-gas at the same time.
2. Description of Related Arts
The fossil fuel power plants are mainly provided for generating and supplying the power or energy for most of the manufactures. For example, the manufacture may burn the coal or oil to produce steam for the steam turbines that drives the electricity generator of the manufacture. The exhaust flue-gas from fossil fuel power plants is well known as one of the main pollution culprits or sources. The flue-gas usually contains a plurality of pollutants or contaminations, such as mercury, sulfur dioxide SO2 or other sulfur oxides; nitrogen oxides NOx—NO and NO2; and carbon dioxide CO2 or other carbon oxides.
Those contaminations directly discharge to the atmosphere without being treated to reduce the contaminated contains has damaged the environment of the earth. For instances, the SO2 and NO2 has caused the acid rainfall, which can damage buildings, historical monuments, and has directly linked to the human health; the nitrogen oxides NOx is also the main reason that cause the Photochemical smog; and the carbon dioxide CO2 has caused the greenhouse effect, which cause the global warming.
In particular, mercury is one kind of heavy metals and is toxic to human beings and animals. Accordingly, large amount of mercury is emitted and polluted to the atmosphere globally, wherein more than 70% of the mercury emission is from coal combustion. Power plants, which are powered by coal combustion, are the major mercury polluting sources globally. Accordingly, mercury and its chemical compounds can enter into the human body through various means such as respiratory, skin and digestive system, resulting in nerve poisoning and human tissue lesions. Since mercury can cumulate in human body for many years, the toxicity may take years to damage the human body. Although the average mercury content in the coal is about 220 ng/g, there requires an enormous amount of coal to complete the coal combustion. As a result, the amount of mercury emission will be rapidly increased, while ecological environment and human health will be concerned due to the mercury pollution. In particular, there are major forms of mercury in the flue gas during coal combustion, which are elemental mercury (Hg0) and mercuric compound (HgCl2, HgO). The industrial mercury control generally uses mercury adsorption to control the amount of mercury emission, such as active carbon adsorption, or calcium-based substance, fly ash, and mineral adsorbents. However, due to the low melting point of elemental mercury, high equilibrium vapor pressure, and low water solubility, mercury cannot be effectively removed from the flue gas. In fact, more than 60% of mercury and its compound in the flue gas will directly release to the atmosphere.
In order to better protect the environment, there are variety of treatments and processes for reducing and minimizing the contamination amount of the industrial wastes mainly from the flue-gas. Traditionally, most of the existing methods for removing the contaminations of the flue-gas are focusing on separately removing the SO2 and NOx. There are mainly two types of flue-gas purification for the treatment of removing the sulfur oxides: dry method and wet method of gas purification technologies.
Take the dry desulfurization for instance. The dry desulfurization usually employs solid absorbent or catalyst for removing the sulfur dioxide SO2 of the waste, such as activated carbon adsorption, molecular sieve adsorption, oxidation, and metal oxidation adsorption etc. The advantage of the dry desulfurization is that no discharging of waste water, and/or waste acid, so that the dry desulfurization is able to minimize and reduce the secondary pollution thereof However, the main concerns are the desulfurization efficiency is low, the equipments of dry desulfurization are bulky and occupy dramatic large space thereof, and the cost of the equipment and it process is high.
Take the wet desulfurization as another example of gas purification. The wet desulfurization for removing the sulfur oxides SO2 includes the limestone-gypsum method, sodium alkali absorption method, ammonia absorption, aluminum method, catalytic oxidation, and catalytic reduction methods. The wet method of the limestone-gypsum method is commonly used worldwide and is the most mature technology for removing the sulfur oxides nowadays.
The limestone-gypsum method is highly efficient of desulfurization and is stable during the process of desulfurizing. The absorbent used in the limestone-gypsum has highly absorbing rate, which is suitable for large amount of waste with high concentration of the sulfur oxides gas, and has high adaptability of the coal. The absorbent of the limestone-gypsum wet method is low in cost. The side products generated from the limestone-gypsum process are able to be utilized for other commercial purposes.
Although the limestone-gypsum method is currently one of the most popular methods having the above mentioned advantages, the limestone-gypsum wet method still occupies too much space and high in manufacturing cost. The process also requires a large amount of water, and generate great amount of waste water and other waste gases, such as waste carbon dioxide and other greenhouse gases, so that it brings the issue of serious secondary pollution. The side products of the wet desulfurization treatment are usually wet, so that it is relatively more difficult for treating the side products therefrom. The waste water from the wet process of the limestone-gypsum has to be treated before discharging. Therefore, the cost of the treatment of the wastes is again increased.
There are relatively more flue-gas treatment technologies for removing the nitrogen oxides, such as selective catalytic reduction (SCR), liquid absorption, microbial absorption, non-selective catalytic reduction, carbon reduction method, catalytic decomposition method, liquid membrane method, SNRB denitrification technology, and feedback oxidation adsorption denitrification technology etc. However, there is only the selective catalytic reduction (SCR) method has been widely applied for the waste treatments.
The selective catalytic reduction method is using the NH3 as the reducing agent to selectively react the NOx of the waste via catalyst to form non-toxic and pollution free N2 and H2O. Under the temperature range of 200 to 400° C. and the stoichiometric ration of 1:1 of NH3 to NOx, the removal rate of the NO is as high as 80 to 90%. However, the catalyst used in this process is high poisoning; and the porous surface of the catalyst tends to be easily clogged up, which is critical to catalyzing reaction, to gradually decrease the removal rate thereof, so that the process is unstable, consumes a large amount of catalyst, and high in operative cost. Furthermore, the selective catalytic reduction method is not suitable for high capacity and high concentration of the NOx of the waste.
Although the mainstream of the industrial process of flue-gas purification is using wet method for removing the sulfur oxides, and using dry method for removing the NOx, there are some other methods for removing both sulfur oxides and nitrogen oxides. For examples, plasma, electron beam method, CuO method, SNAP method etc. Those methods for moving both SOx/NOx at the same time are looking for a treatment that is more efficient and more economic than the methods of separately treating the SON and NOx. Some of the method for removing both SOx/NOx may be able to achieve the desired removal rate. For instance, the industrial art of removing both SOx/NOx could be performed by the lime/limestone flue-gas desulfurization FGD system, which is used for removing the SO2 while using the catalytic method SCR for removing the NOx. The above mentioned method for removing both SOx/NOx is able to remove 90% of sulfur dioxide and 30 to 80% of nitrogen oxides and combines the wet and dry method, so that the FGD system of the wet method and the SCR system of the dry method are able to independently remove its respective targeted contaminations to achieve each contaminations desired removal rate. It is worth mentioning that the methods for removing both SOx/NOx are adsorption method, electron beam desulfurization (EBD), pulse induced plasma chemical process (PPCP), and liquid-membrane method.
However, the method for removing both SOx/NOx via combining the wet and dry methods also inherited the disadvantages of both wet and dry methods as mentioned above. Therefore, the method for removing both SOx/NOx tends to be costly in both equipment and operation, require a large amount of water, and have secondary pollution. The activity of the catalyst is gradually decreasing, so that the removing rate keeps decreasing. Most important of all, none of the existing methods consider to remove the carbon dioxide separately or remove the SOx/NOx and the carbon dioxide at the same time.